brake

brake¹

—brakeless, adj.

/brayk/, n., v., braked, braking.

n.

1. a device for slowing or stopping a vehicle or other moving mechanism by the absorption or transfer of the energy of momentum, usually by means of friction.

2. brakes, the drums, shoes, tubes, levers, etc., making up such a device on a vehicle.

3. anything that has a slowing or stopping effect.

4. Also called brakeman. a member of a bobsled team who operates the brake.

5. Also called breaker. a tool or machine for breaking up flax or hemp, to separate the fiber.

6. Also called press brake. a machine for bending sheet metal to a desired shape.

7. Obs. an old instrument of torture.

v.t.

8. to slow or stop by means of or as if by means of a brake.

9. to furnish with brakes.

10. to process (flax or hemp) by crushing it in a brake.

v.i.

11. to use or run a brake.

12. to stop or slow upon being braked.

13. to run a hoisting machine.

[1400-50; late ME < MD, MLG; akin to BREAK]

Syn. 8. halt, arrest, stay, restrain; curb, curtail.

brake²

/brayk/, n.

a place overgrown with bushes, brambles, or cane.

[1400-50; late ME (in phrase brake of fern thicket of fern) < MLG brake thicket]

brake³

/brayk/, n.

any of several large or coarse ferns, esp. the bracken, Pteridium aquilinum.

[1275-1325; ME brake, prob. by back formation from braken BRACKEN, taken as pl.]

brake⁴

/brayk/, v. Archaic.

pt. of break.

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Device for decreasing the speed of a body or stopping its motion.

Most brakes act on rotating mechanical elements and absorb kinetic energy mechanically, hydrodynamically, or electrically. Mechanical brakes are the most common; they dissipate the kinetic energy as heat generated by mechanical friction between a rotating drum or disk and a stationary friction element. A hydrodynamic (fluid) brake has a rotor (rotating element) and a stator (stationary element). Resistance to rotation is created by fluid friction and circulation of the liquid (usually water) from a series of pockets in the rotor to a series of complementary pockets in the stator. See also air brake.

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▪ machine component

      device for decreasing the speed of a body or for stopping its motion. Most brakes act on rotating mechanical elements and absorb kinetic energy either mechanically, hydrodynamically, or electrically.

      Mechanical brakes are the most common; they dissipate kinetic energy in the form of heat generated by mechanical friction between a rotating metallic drum or disk and a stationary friction element brought into contact with it by mechanical, hydraulic, or pneumatic means. The friction elements for drum brakes may be bands or shoes (blocks with one concave surface); for disk brakes they are pads or rings. Friction materials may be organic, metallic, or ceramic; molded asbestos is commonly used.

      Mechanical operation by means of rigid links is satisfactory for single brakes, but when several brakes are actuated from a single source, as on an automobile, it is difficult to obtain equal braking effectiveness on all wheels; for this reason, hydraulic actuation, with oil under the same pressure acting on all brakes, is preferable. The braking of railroad cars is effected by cast-iron shoes that bear directly on the circumference of the wheels and are activated by compressed air (see air brake).

      A hydrodynamic (fluid) brake has a rotor (rotating element) and a stator (stationary element) that resemble the impeller and runner in a hydraulic coupling. Resistance to rotation is created by fluid friction and circulation of the liquid (usually water) from a series of pockets in the rotor to a series of complementary pockets in the stator. Because the resistance to rotation—i.e., braking power—depends on the speed of the rotor, these brakes cannot completely stop a rotating member; however, if means for cooling the liquid are provided, they can dissipate large amounts of kinetic energy in a very effective manner.

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